Remove status-utf8 option

It is incorrect to set it at all because what powerline outputs depends on 
locale used, and if locale is utf8 then tmux should already set this option.

powerline/bindings/tmux/powerline-base.conf

@@ -1,5 +1,4 @@
 set -g status on
-set -g status-utf8 on
 set -g status-interval 2
 set -g status-left-length 20
 set -g status-right '#(env "$POWERLINE_COMMAND" $POWERLINE_COMMAND_ARGS tmux right -R pane_id=\"`tmux display -p "#D"`\")'